Search Results (374)

Electrochemical treatment can provide contaminant destruction, phase separation, ionic polishing, and resource recovery; however, performance cannot be judged by removal efficiency alone. This structured critical review compares electro-oxidation (EO), electrocoagulation (EC), electro-Fenton (EF), electrodialysis (ED), electrodeionization (EDI), capacitive deionization (CDI), flow-electrode CDI (FCDI), and bioelectrochemical systems (BES) in municipal wastewater, industrial effluents, sludge-related applications, and treatment side-streams. Searches of Scopus, Web of Science Core Collection, and PubMed were updated to 22 July 2026, and the evidence was assessed according to treatment function, wastewater realism, operating mode, durability, residual fate, energy and cost boundaries, resource recovery, and life cycle implications. Recent advances include porous flow-through anodes, oxygen-efficient cathodes, selective ion separation materials, and pilot BES configurations. However, scale-up remains constrained by electrode aging, by-products, sludge and concentrate management, oxygen transfer, fouling, competing ions, internal resistance, biological instability, and incomplete long-term economic and environmental evidence. The quantitative results show that the energy, cost, and carbon outcomes depend strongly on the treatment function and system boundary. The evidence for sludge and biosolids is less mature than that for liquid wastewater. Therefore, electrochemical technologies are best positioned as function-specific units within hybrid treatment trains rather than as universal replacements for conventional treatments. Full article

South Africa possesses substantial bioenergy potential derived from agricultural residues, forestry by-products, municipal organic waste, wastewater sludge, and dedicated energy crops, positioning bioenergy as a potentially important contributor to the country’s low-carbon energy transition. Despite more than two decades of supportive policy, modern bioenergy remains a marginal contributor to the country’s energy system. Although previous studies have examined individual bioenergy technologies, feedstocks, environmental impacts, or policy frameworks, a comprehensive assessment of the alignment between policy ambition, technological readiness, implementation outcomes, and emerging sustainable development opportunities in South Africa remains lacking. This review presents a systematic integrative review of bioenergy development in South Africa, evaluating the alignment between policy ambition, technological readiness, and implementation outcomes. Literature published between 2000 and 2025 was systematically reviewed using Scopus, Web of Science, Google Scholar, and institutional publications. A PRISMA-informed screening process identified 427 records, of which 116 studies met the inclusion criteria for detailed synthesis. Evidence was synthesized across three interconnected dimensions: (i) policy and regulatory frameworks, (ii) feedstock availability and technological readiness, and (iii) deployment outcomes, implementation challenges, and future development opportunities. The findings reveal a persistent implementation gap despite abundant biomass resources and commercially established bioenergy conversion technologies Although global biofuel production exceeded 180 billion liters in 2023, South Africa’s installed bioenergy electricity capacity remains approximately 265 MW, representing less than 0.5% of the country’s approximately 60 GW installed electricity generation capacity. By comparison, installed solar and wind capacities exceed 8 GW and 3 GW, respectively. The review identifies fragmented governance, limited investment incentives, regulatory uncertainty, infrastructure constraints, and inadequate integration of bioenergy into national energy planning as the principal barriers to deployment. The review concludes that South Africa’s principal challenge is not biomass availability or technological capability, but translating policy ambition into coordinated implementation capable of scaling sustainable bioenergy deployment. Full article

Casimicrobium huifangae SJ-1 is one of the 28 core microbial groups in the activated sludge of municipal wastewater treatment plants. It exhibits strong environmental adaptability and interactions with other microbes. To develop a genetic manipulation system for this strain, we tested several broad-host-range plasmids, and pBBR1MCS-2 was successfully transformed into strain SJ-1. However, only the plasmid extracted from the transformant could be retransformed into strain SJ-1, suggesting strong host defense systems. We investigated the genome-wide DNA methylation and obtained a DNA methylation map and nine methylation-targeting motifs from C. huifangae. A modified pBBR1MCS-2 lacking all targeting motifs achieved transformation efficiency comparable to that of the host-derived plasmid, implicating the restriction modification (R-M) barrier of C. huifangae. REBASE annotation revealed nine R-M systems in the genome, including two of Type I, six of Type II, and one of Type III. Quantitative PCR showed that the restriction endonuclease component of the Type I RM-C system was transcriptionally upregulated in the transformant harboring pBBR1MCS-2. The subunits responsible for the methyltransferase and endonuclease functions of RM-C were expressed in Escherichia coli, purified, and characterized. The targeting motif of RM-C was implicated as 5′-GAGNNNNNNNTGCT-3′ based on in vitro cleavage assays and SMRT methylation calls. These findings reveal the DNA methylation characteristics of C. huifangae SJ-1 and outline the possible methylation-based defense architecture, providing a reference for future genetic manipulation. Full article

This article examines the comprehensive assessment of the environmental and economic performance and social significance of wastewater treatment plants (WWTPs), using a company in Western Kazakhstan as an example. During the analysis of the treatment plant’s performance, the potential for using activated sludge as an alternative energy source was explored. Initially, it was found that activated sludge could be used as boiler fuel at the treatment plant. In the future, after drying the sludge, it could be used to replace coal at combined heat and power plants (CHPs) when production is set up. The article analyzes international research and modern approaches to sustainable water use and municipal and industrial wastewater treatment. The paper examines the role of wastewater treatment facilities in minimizing anthropogenic impacts on ecosystems and reducing production costs. It also assesses the prospects for greening protected areas and the social impact of modernizing the region’s infrastructure. The research aims to optimize wastewater treatment facilities through the conservation of resources, water reuse and the use of energy-saving technologies. Practical recommendations have been developed to improve the efficiency and sustainability of wastewater treatment plants, taking into account the climatic conditions of Western Kazakhstan. Water conservation is a goal of sustainable development. Conserving water resources through high-efficiency treatment plants will save natural water, which is also the goal of this study. The article’s materials may be useful for specialists in water management, environmental policy, environmental design, and regional planning. Full article

The high-rate contact stabilization–activated sludge (HiCS–AS) process, which integrates an upstream high-rate contact stabilization process with a downstream activated sludge process, is a promising approach for enhancing energy recovery from municipal wastewater. This 16-week continuous study evaluated the organic matter recovery capacity and process stability of a HiCS–AS process, configured as a sequencing batch reactor, under realistic conditions where water temperatures decreased from 29 °C to 14 °C. The upstream HiCS process, operating at a solids retention time of 0.60 days, exhibited stable sludge settling behavior and achieved a stable carbon recovery rate of 0.23 ± 0.04 g-COD/g-COD. The overall COD removal rate for the system was 86% ± 3%, and the HiCS–AS process demonstrated a statistically significant increase in organic matter recovery compared to a parallel single activated sludge process (paired Student’s t-test, p < 0.05). These findings indicate that the HiCS–AS process provides a consistent and effective approach to organic matter recovery compared to conventional processes. Full article

The article presents an energy, economic and environmental (3-E) analysis of a reference wastewater treatment plant (WWTP) with a capacity of 200,000 population equivalent (PE). The analysis includes sewage sludge treatment, anaerobic digestion (AD), combined heat and power (CHP), and mono-incineration of solar-dried sludge. The specific investment cost for the reference WWTP is 435 €/PE. Annual costs for operation and maintenance are estimated at 26 €/(PE·y) and the energy costs are 5 €/(PE·y). The annual energy demands are 32 kWh_el/(PE·y) of electricity and 14 kWh_th/(PE·y) of thermal energy for digesters’ heating. For a specific sludge quantity of 20 kg_DS/(PE·year), the biogas production is 245 Nm³/t_DS or 5 m³/(PE·y). Biogas-driven CHP supplies 10.3 kWh/(PE·year) of electricity and 14.7 kWh/(PE·year) of thermal energy, which meets 30% of the electrical demand and 100% of the thermal energy demand. Total (capital and operation) costs of sludge mono-incineration are evaluated at 300 €/t_DM or 6 €/PE. The heating value of digested and solar-dried sludge is 2 kWh/kg_WM. The total cost of the solar drying system is 30 €/PE while the sludge solar drying rate is 370 kg_DM/(m²·y). The environmental analysis showed that the on-site carbon footprint of the reference WWTP is 50 kg_CO2eq/(PE·y), with the largest contributions arising from N₂O emissions during wastewater treatment, CO₂ from sludge mono-incineration, and CO₂ from biogas combustion in the CHP unit. Full article

Anaerobic co-digestion (AcoD) is a promising strategy to enhance biogas production and improve the sustainability of wastewater treatment plants (WWTPs). However, information regarding process scale-up and reactor performance following the interruption of co-substrate feeding remains limited. This study evaluated the anaerobic co-digestion of municipal mixed sludge (MMS) and fruit and vegetable peel purées (FVPP) in a 10.6 L semi-continuously fed continuously stirred tank reactor (CSTR), operating under conditions representative of municipal WWTP anaerobic digesters. Mono-digestion (AMD) and co-digestion (AcoD) assays were conducted under mesophilic conditions and assessed through process performance indicators. AcoD increased methane concentration from 58.50% to 60.75%, while total volatile solids (TVS) removal efficiency increased from 41.67% to 59.84% in comparison with AMD. Total chemical oxygen demand (COD_T) removal efficiency also improved from 40.82% to 56.48%. Furthermore, H₂S concentrations decreased from approximately 350 ppmv during mono-digestion to 7 ppmv during co-digestion. An additional mono-digestion trial (aAMD) performed after co-substrate withdrawal achieved the highest specific methane production (0.27 L CH₄/g⁻¹ TVS) and organic matter removal efficiencies (63.73% for TVS and 67.55% for COD_T, respectively). These results demonstrate that co-digestion of MMS and FVPP improves methane quality, enhances organic matter removal, and reduces H₂S emissions, while maintaining stable reactor performance under scale-up conditions and after the interruption of co-substrate feeding. Full article

Anaerobic digestion of municipal wastewater sludge is often limited by slow hydrolysis rates. This study evaluated the effects of ozone pretreatment on methane production during mesophilic batch digestion. Ozone was applied at 0–10% for 30–90 s, with inoculum-to-substrate ratios of 1.0–2.0. Methane production was monitored using the AMPTS II system. The maximum methane yield (736 NmL CH₄ g⁻¹ VS; 1381 NmL total) was obtained at 10% ozone for 30 s and I/S = 1.5. Kinetic modelling showed enhanced methane production rates and reduced lag phases, with the Gompertz and Logistic models providing the best fit. Full article

In the face of the raw materials crisis and environmental concerns, sustainable waste management has become a priority for current and future generations. Recycling waste from wastewater treatment plants in a closed loop protects natural resources, reduces landfill volumes, and lowers disposal costs. This paper presents the results of tests on the physical, filtration, and mechanical properties of mixtures of washed mineral waste (WMW) from grit chambers with fly ash from the thermal treatment of municipal sewage sludge (SSA) in a fluidized bed furnace. Additionally, radiological tests of the mixture components were conducted. Based on the conducted tests, the possibility of sustainable use in civil engineering, such as soil backfills and embankment construction materials, was assessed. The possibility of safely using waste materials in the indicated construction solutions was demonstrated for mixtures with dominant WMW content (90% and 70% by total weight). The waste mixtures correspond to poorly or medium-grade sands with a small amount of silt (uniformity coefficients of 3.33, 3.50, and 8.00). They are characterized by maximum dry densities of 1.542, 1.770, and 1.780 g/cm³; optimal moisture contents of 12.54, 12.86, and 20.25%; permeability coefficients of 0.08, 0.22, and 0.39 m/d; and internal friction angles of 38.4, 39.5, and 40.1°. The values of the determined parameters of some mixtures are similar to those of natural sands used as construction aggregates. All mixtures meet the geotechnical criteria for use in road embankments, below frost depth, and in flood embankment bodies. Mixtures with a 90% mass fraction of WMW were also approved for application as backfill for installation trenches. However, none of the mixtures met the hydraulic conductivity threshold required for the upper layers of embankments nor for backfill of abutments and retaining structures without the use of an additional binder (cement or lime), which is considered a prerequisite for these applications. Full article

To address the problems of short-circuit flow and dead zones, complicated operation and control caused by intermittent influent, and the mismatch between aeration rate and oxygen demand in the Cyclic Activated Sludge System (CASS), a novel Multi-Compartment Fixed-Biofilm Cyclic Activated Sludge System (MCFCASS) was developed. This system operated in continuous-flow mode, and the aeration rate of each compartment was redistributed using a mathematical model. The results show that the plug flow ratio of the MCFCASS reactor increased from 18.75% to 31.25% compared with the CASS reactor. After aeration rate redistribution, the average total nitrogen (TN) removal efficiency of the MCFCASS reactor rose from 83.34% to 86.80%, and the effluent TN concentration consistently met the Grade I-A limit (15 mg/L) specified in the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002). The average removal efficiencies of chemical oxygen demand (COD) and ammonium nitrogen (NH₄⁺-N) increased from 91.58% and 93.39% to 92.98% and 94.57%, respectively. Microbial community analysis revealed that after aeration rate redistribution, the relative abundances of Pseudomonadota, Bacteroidota, and Bacillota in the pre-reaction zone of MCFCASS were 39.17%, 17.78%, and 10.33%, respectively. In addition, the abundances of some functional bacterial groups in the first and fourth compartments of the main reaction zone shifted adaptively in response to the aeration rate redistribution, consistent with the trends in pollutant removal contributions in these compartments. Hierarchical clustering and principal coordinate analysis (PCoA) further indicated that aeration rate redistribution influenced the microbial community structure. The above laboratory-scale optimization results may provide a preliminary reference for aeration control and improvement of denitrification performance in similar processes. Full article

Industrial and municipal wastewater may contain substances that inhibit biological processes in wastewater treatment plants (WWTPs), posing risks to operational stability and environmental protection. The aim of this study is to evaluate the practical suitability of the ISO 8192:2007 respiration inhibition test for assessing the toxicity of wastewater. Nitrified activated sludge from a municipal WWTP was used to analyze wastewater from three industrial companies, wastewater from several discharge locations at a hospital, and WWTP influent. Oxygen consumption and inhibition were determined at sample-specific dilution levels and the reference substance 3,5-dichlorophenol. Two samples from the dental department of the hospital showed toxic effects on activated sludge respiration (inhibition > 50%), while no toxic effects were observed in the remaining samples. Several samples exhibited stimulatory effects (inhibition < 0%), indicating the presence of readily biodegradable organic matter. However, inhibitory effects (0–50% inhibition) were detected in individual wastewater samples at higher concentrations. This demonstrates that the method can detect toxicological changes in wastewater and is suitable for routine monitoring and early warning in WWTPs. Full article

Improving the effluent quality of municipal wastewater treatment plants (WWTPs) is essential for sustainable water management and water quality protection in the Yellow River Basin. Many existing WWTPs in northern China were constructed under earlier discharge requirements and now face dual challenges of stricter effluent standards and poor low-temperature performance in winter. In this study, a municipal WWTP with a design capacity of 5 × 10⁴ m³/d in northern China was upgraded to improve winter treatment performance and support stable compliance with the discharge requirements of the Yellow River Basin. The original anaerobic + oxidation ditch process suffered from unstable effluent quality, excessive sludge loading, and insufficient pollutant removal under low-temperature conditions. A land-saving retrofit strategy was therefore proposed, involving oxidation ditch wall-height raising to extend the hydraulic retention time (HRT) and membrane bioreactor (MBR) integration to increase the mixed liquor suspended solids (MLSS) concentration. After the retrofit, the total HRT increased to 19.82 h, and the average MLSS concentration reached 7050 mg/L. The relative abundances of key nitrogen-removing bacteria, including Nitrospiraceae, Nitrosomonadaceae, and Rhodocyclaceae, increased markedly. Meanwhile, denitrification sludge loading and BOD₅ sludge loading decreased to 0.030 and 0.033 kg/(kg·d), respectively. Under low-temperature conditions, the theoretical removal capacities of total nitrogen (TN) and BOD₅ reached 44.32 and 286.19 mg/L, respectively, enabling stable effluent compliance. The results show that this retrofit strategy can improve WWTP effluent quality while avoiding large-scale land expansion, providing a practical and sustainable solution for upgrading cold-region WWTPs along the Yellow River Basin. Full article

Deammonification, which is based on partial nitritation and anammox (PN/A), is a well-established sidestream treatment for nitrogen removal. However, transferring deammonification to mainstream wastewater treatment remains challenging due to low temperatures, the need to retain slow-growing anammox bacteria (AnAOB), and their competition for nitrite with nitrite-oxidizing bacteria (NOB) and heterotrophic denitrifiers. This work investigates cubic polyurethane foam carriers to promote growth and retention of AnAOB. A moving bed biofilm reactor (MBBR) and an integrated fixed-film activated sludge (IFAS) reactor were compared over a three-year experimental period at lab-scale. The feasibility of the biofilm carriers for deammonification was first evaluated under sidestream conditions, followed by a stepwise transition to mainstream operational conditions. The impact of operational parameters, including dissolved oxygen concentration, pH value, and aeration strategy, was evaluated with respect to the activity of aerobic ammonium-oxidizing bacteria (AOB), NOB, and AnAOB, as well as nitrogen removal rates. Deammonification reached nitrogen removal rates of 0.04–0.12 kg N m⁻³ d⁻¹ (IFAS reactor) and 0.02–0.28 kg N m⁻³ d⁻¹ (MBBR) at subphases with reactor bulk concentrations above 60 mg NH₄-N L⁻¹. Highest nitrogen removal degrees of 77 ± 6% (IFAS) and 76 ± 5% (MBBR) were achieved at reactor bulk concentrations of 96 mg NH₄ L⁻¹ and 97 mg NH₄ L⁻¹, respectively. Lower concentrations triggered NOB activity in both reactors, leading to an increase in nitrate concentration up to 22 mg NO₃-N L⁻¹. AOB and AnAOB activities were on average 6-fold higher on the carriers compared to suspended biomass throughout all experimental phases, demonstrating the feasibility of using cubic polyurethane foam carriers for deammonification. This was also confirmed by fluorescence in-situ hybridization (FISH) measurements. Median nitrogen removal rates over all experimental phases of 0.07 kg N m⁻³ d⁻¹ for the IFAS reactor and 0.05 kg N m⁻³ d⁻¹ for the MBBR were achieved, which are comparable to conventional activated sludge systems performing nitrogen removal via nitrification–denitrification. While at lower nitrogen concentrations, the IFAS reactor yielded superior nitrogen removal rates, peak nitrogen removal rates of 0.28 kg N m⁻³ d⁻¹ were measured in the MBBR configuration. However, controlling NOB activity at lower temperatures and concentrations remains a challenge in MBBR and IFAS configurations. In our study, in the IFAS reactor NOB activities were visible on fewer days than in MBBR. At mainstream-like conditions, higher nitrogen removal rates of IFAS (0.09–0.12 kg N m⁻³ d⁻¹) were achieved compared to the MBBR (0.06–0.09 kg N m⁻³ d⁻¹). This demonstrates the advantage of the IFAS reactor in treating mainstream wastewater via deammonification. As an autotrophic nitrogen removal process, the implementation of deammonification in the mainstream of municipal wastewater treatment plants enables enhanced recovery of biogas from sewage organic matter. The latter would otherwise be consumed during the conventional nitrification-denitrification pathway. Consequently, the overall energy balance for wastewater treatment can be improved, contributing to a more environmentally sustainable process. Full article

This study systematically compared the performance of different composite magnetic materials in enhancing activated sludge treatment of municipal wastewater. A sequencing batch reactor (SBR) process was used as the model system. Four different composite magnetic materials were examined: Fe₃O₄ composite activated carbon, Fe₃O₄ composite diatomite, Fe₃O₄ composite composite kaolin, and Fe₃O₄ composite composite fly ash. Their performance in enhancing activated sludge treatment of municipal wastewater was evaluated in terms of pollutant removal, sludge physicochemical properties, and molecular biology analysis. Furthermore, the two best-performing composite magnetic materials were further investigated at different dosages to examine their pollutant removal performance and mechanisms. Furthermore, the two best-performing composite magnetic materials were further investigated at different dosages to examine their pollutant removal performance and mechanisms. The results showed that, compared with the control system (without material addition), the addition of four composite magnetic materials improved the average removal efficiencies as follows: for the Fe₃O₄ composite activated carbon, Fe₃O₄ composite diatomite, Fe₃O₄ composite kaolin, and Fe₃O₄ composite composite fly ash systems, COD removal increased by 2.55%, 2.77%, 1.67%, and 4.10%, respectively; TN removal increased by 1.71%, 3.33%, 4.82%, and 0.82%, respectively; and TP removal increased by 4.96%, 7.02%, 6.01%, and 5.76%, respectively. In the Fe₃O₄ composite diatomite system, the highest average removal efficiencies of COD, TN, and NH₄⁺-N were achieved at a dosage of 50 mg/L, whereas the highest average TP removal efficiency was achieved at a dosage of 200 mg/L. In the Fe₃O₄ composite kaolin system, the highest average removal efficiencies of COD, TP, and NH₄⁺-N were achieved at a dosage of 50 mg/L, while the highest average TN removal efficiency was achieved at a dosage of 200 mg/L. High-throughput sequencing indicated that the highest activity of denitrifying genera was observed in the Fe₃O₄ composite diatomite system at a dosage of 50 mg/L and in the Fe₃O₄ composite kaolin at a dosage of 200 mg/L, respectively. The addition of composite magnetic materials enhances the efficiency of municipal wastewater biological treatment. These findings provide theoretical and technical guidance for the selection of magnetic composite materials in municipal wastewater treatment. Full article

In municipal wastewater treatment plants (WWTPs), anaerobic digestion of municipal mixed sludge (MMS) often yields low energy recovery and operational instability due to imbalances between primary and secondary sludges. Anaerobic co-digestion (AcoD) with readily biodegradable wastes, such as fruit and vegetable waste (FVW), can enhance process stability and biogas production. Life cycle assessment (LCA) methodology is used in this study to evaluate the environmental performance of implementing AcoD of MMS and FVW in a municipal WWTP, compared with a business-as-usual scenario combining mono-digestion of MMS and incineration of FVW. The LCA was modelled in openLCA 2.5 using the ecoinvent 3.9.1 database (cut-off allocation approach), and impacts were assessed with the ReCiPe 2016 Midpoint (H) method, focusing on climate change, terrestrial acidification, fossil fuel depletion, and marine eutrophication. Results indicate that AcoD reduces impacts across all environmental categories, mainly due to higher biogas yields that increase on-site electricity generation and decrease reliance on grid electricity. Improved total solids removal also lowers digestate production and composting-related burdens. Electricity consumption remains the main hotspot in both scenarios, highlighting the importance of energy efficiency and electricity mix. Sensitivity analysis on methane content (61–65% v/v) confirms the robustness of AcoD’s environmental benefits. Full article